[llvm-commits] CVS: llvm/docs/FAQ.html

[Chris Lattner]

Changes in directory llvm/docs:

FAQ.html updated: 1.36 -> 1.37
---
Log message:

Answer the FAQ: "can llvm convert C++ code to C?"


---
Diffs of the changes:  (+58 -1)

 FAQ.html |   59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 58 insertions(+), 1 deletion(-)


Index: llvm/docs/FAQ.html
diff -u llvm/docs/FAQ.html:1.36 llvm/docs/FAQ.html:1.37
--- llvm/docs/FAQ.html:1.36	Wed Apr 26 16:03:17 2006
+++ llvm/docs/FAQ.html	Wed Jul 19 13:19:59 2006
@@ -79,6 +79,8 @@
     How can I disable all optimizations when compiling code using the LLVM GCC front end?
     </li>
 
+    <li><a href="#translatec++">Can I use LLVM to convert C++ code to C code?</a></li>
+
   </ol>
   </li>
 
@@ -501,6 +503,61 @@
 </p>
 </div>
 
+
+<div class="question">
+<p>
+<a name="translatec++">Can I use LLVM to convert C++ code to C code?</a>
+</p>
+</div>
+
+<div class="answer">
+<p>Yes, you can use LLVM to convert code from any language LLVM supports to C.
+Note that the generated C code will be very low level (all loops are lowered
+to gotos, etc) and not very pretty (comments are stripped, original source
+formatting is totally lost, variables are renamed, expressions are regrouped), 
+so this may not be what you're looking for.  However, this is a good way to add
+C++ support for a processor that does not otherwise have a C++ compiler.
+</p>
+
+<p>Use commands like this:</p>
+
+<ol>
+<li><p>Compile your program as normal with llvm-g++:</p></li>
+
+<div class="doc_code">$ llvm-g++ x.cpp -o program</div>
+
+<p>or:</p>
+
+<div class="doc_code">
+ llvm-g++ a.cpp -c
+ llvm-g++ b.cpp -c
+ llvm-g++ a.o b.o -o program
+</div>
+
+<p>With llvm-gcc3, this will generate program and program.bc.  The .bc file is 
+the LLVM version of the program all linked together.</p>
+
+<li><p>Convert the LLVM code to C code, using the LLC tool with the C
+backend:</p></li>
+
+<div class="doc_code">$ llc -march=c program.bc -o program.c</div>
+
+<li><p>Finally, compile the c file:</p></li>
+
+<div class="doc_code">$ cc x.c</div>
+
+</ol>
+
+<p>Note that, by default, the C backend does not support exception handling.
+If you want/need it for a certain program, you can enable it by passing
+"-enable-correct-eh-support" to the llc program.  The resultant code will
+use setjmp/longjmp to implement exception support that is correct but
+relatively slow.
+</p>
+</div>
+
+
+
 <!-- *********************************************************************** -->
 <div class="doc_section">
   <a name="cfe_code">Questions about code generated by the GCC front-end</a>
@@ -614,7 +671,7 @@
   src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
 
   <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
-  Last modified: $Date: 2006/04/26 21:03:17 $
+  Last modified: $Date: 2006/07/19 18:19:59 $
 </address>
 
 </body>